Electric Clock. Bentley R Type / R-R Silver Dawn
N.W.Geeson  I.Eng. M.I.R.T.E    M.S.O.E 

A number of owners report problems with the electric clock operation and frequently the clock does indeed need maintenance, they either require a thorough overhaul because they have failed electrically or lubrication is required because the lubricant has dried up. A number of owners even change the inside of the clock mechanism for a quartz unit. 

On a number of occasions the clock has been connected wrongly, the owner has attempted to change the vehicle polarity or the owner has ignored the requirement to operate the starter push button to initiate the clock start procedure. The images below are intended at least to show the correct wiring connections and the re-start knob. 

 

When the glove box door is lowered the owner will be faced with the view as shown in Fig 1. Note that the rear of the clock is enclosed by a cover held in position by two knurled nuts, as shown in this view. 

A close up of the rear end of the clock is shown in Fig 2. Note in particular the large knurled knob at the 4 o’clock position in this picture. This knob is used to set the correct time initially, but another important function it serves is to start the clock by depressing the end of the knob. The knob may need depressing more than once to set the clock in motion, it must also be understood that if the clock is not started after the battery has been disconnected the clock unit is in a state of stall. 

Obviously the clock will stop when the battery is disconnected and this will include when any battery master switch is moved to the ‘off’ position. The owner may not always remember to operate the re-start button and also specialist repairers do not always realise that the clock must be re-started immediately after the battery is re-connected, when the garage may have previously isolated the battery. To safeguard this situation it is wise to isolate the clock by disconnecting the earth or feed wire, at the clock, before major repairs are undertaken. However if this route is taken by all means advise the garage accordingly that the clock has been disconnected. It is appallingly obvious that many of these clocks are in a stalled condition whilst the car is awaiting collection from the garage by the owner, a condition that the clock detests. 

Clearly the label tells any reader what is likely to happen if the polarity is reversed or the wiring connected incorrectly. A clear “must do” wiring exercise is necessary to those contemplating changing the cars over to negative earth. If you must change to negative earth  please do not contact me with subsequent troubles! 

The view shown in figure 4 is that with which you will be faced when the rear clock protection cover is removed. Note the correct positioning of the wiring……. colours Purple, Black and Green. The long lever in the centre is for fast or slow regulation of the clock. 

It is wise to be warned that these regulators should not be adjusted unless the clock has been timed for at least 5 days whilst connected to a fully charged battery. If the clock runs and keeps time in that situation and yet loses time whilst fitted to the car firstly check the battery voltage and always have the dynamo regulator checked and adjusted before trying to adjust the clock regulator. In addition, be warned that on a car that is infrequently run the clock will always loose time. 

Lastly, it is helpful to know that a clock that starts to lose time suddenly is a good sign that the dynamo, regular or battery are giving trouble even before the actual component has failed. So if you are scheduled to take a long trip and the clock starts to loose time have these three items checked out.